Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$131.29	9.144%	$143.2952	$143.30	$143.30	$143.30
Purchase #2	$41.69	4.602%	$43.6086	$43.61	$43.60	$43.60
Purchase #3	$127.49	3.354%	$131.766	$131.77	$131.75	$131.80
Purchase #4	$111.45	3.731%	$115.6082	$115.61	$115.60	$115.60
Purchase #5	$18.31	10.513%	$20.2349	$20.23	$20.25	$20.20
Purchase #6	$113.67	9.169%	$124.0924	$124.09	$124.10	$124.10
Purchase #7	$250.40	3.138%	$258.2576	$258.26	$258.25	$258.30
7 purchase totals =	$794.30		$836.8629	$836.87	$836.85	$836.90